Several medical laboratory tests make use of patient blood samples. Patient blood often is collected in a vacuum tube (e.g., BD Vacutainer®, Beckton Dickinson) and often is processed for further analysis. Certain blood products, such serum, are prepared by processes that include clotting patient blood. Such blood products can be separated from the clots and then analyzed in a laboratory test. A blood product sometimes is analyzed in one or more laboratory tests for clarity and/or amount of one or more components (e.g., glucose, lipids, drugs, antibodies, elements (e.g., sodium, potassium, chloride, iron), creatinine, urea, hormones, enzymes). A blood product sometimes is analyzed by a spectrometric assay that detects light transmitted through the product.